Polymerization process for styrene rich butadiene/styrene latex paints



United States Patent 3,393,169 POLYMERIZATION PROCESS FOR STYRENE RICHBUTADIENE/STYRENE LATEX PAINTS James Glenn Richards, North Charleston,S.C., and Jack Fred Elder, Houston, Tex., assiguors to Ashland Oil &Refining Company, Houston, Tex., a corporation of Kentucky No Drawing.Continuation-impart of application Ser. No. 100,500, Apr. 4, 1961. Thisapplication June 26, 1964, Ser. No. 378,452

Claims. (Cl. 260-293) ABSTRACT OF THE DISCLOSURE A method for producingan aqueous paint product having freeze thaw stability sufiicient towithstand two freeze thaw cycles comprising forming an emulsionpolymerization system of about 42-25% butadiene 1,3 and about 58-75% byweight of an aryl olefin, polymerizing all of the butadiene and part ofthe aryl olefin, about 1050% by weight of the total aryl olefin beingwithheld, to an initial conversion of about to about thereafter addingthe withheld aryl olefin to the resultant emulsion system polymerizinguntil substantially conversion is obtained.

This application is a continuation-in-part of United States patentapplication Ser. No. 100,500, filed Apr. 4, 1961, and now abandoned.

This invention relates to paint latexes and water dispersion paintcompositions containing such paint latexes. More particularly, itrelates to an improved method for producing paint latexes which areinherently more freeze stable than those heretofore employed in waterdispersion paint compositions.

In recent years, Water dispersion paint compositions in which syntheticlatexes prepared by emulsion polymerization are employed as binders havebecome widely accepted for both inside and outside applications. Theadvantages in application as well as the desirable characteristics ofthe resultant coatings or films are Well recognized both within andwithout the paint manufacturing industry. Unfortunately, however, suchpaint compositions are also plagued by certain disadvantages, not theleast of which is their general inability to Withstand reducedtemperatures ranging from freezing to considerably below freezing. Undersuch temperature conditions, thickening or coagulations occurs,rendering the compositions useless for coating purposes. Both the latexand paint manufacturers, therefore, have been confronted with thenecessity of improving the freeze resistance or freeze stability ofpaint latexes and paint compositions to an extent sufiicient for suchproducts to withstand naturally and frequently occurring lowtemperatures without detriment.

To this end, it has been proposed to incorporate in such latexes any ofthe well known freezing point-depressing alcohols and glycols and/or anyof various chemical additives which have, from time to time, been foundto impart to such latexes a measure of resistance or stability to theotherwise deleterious effects of repeated freezing. Among such additivesmost generally employed are any of various nonionic and anionicemulsifying agents or, more preferably, a combination of the two. Theseare usually incorporated in the latex as post polymerization additivesalthough it is also beneficial to have at least a portion of theadditive present during polymerization. Certain of such additives haveproved to be eifective freeze stabilizing agents and have received widecommercial acceptance. Still others, however, have not been completelysatisfactory because they do not provide adequate protection at lowertemperatures, or for any of various other reasons. In either event, itis apparent that if paint latexes could be produced with improvedinherent freeze stability properties, the effectiveness of suchadditives would be enhanced.

The present invention is concerned with producing such inherently morefreeze stable paint latexes. Accordingly, it is a principal object ofthis invention to provide a methed for attaining this end. It is afurther object of this invention to provide an improved method forpolymerizing a conjugated diolefin and a monoethylenic compoundpolymerizable therewith which will produce a more freeze stable polymerfor use in water dispersion paint compositions. It is a still furtherobject of this invention to provide an improved polymerization methodwhich is economical, requires little if any additional supervision, andmay be practiced in conventional polymerization equipment. A furtherobject is to provide latexes of such a nature as will enhance theeffectiveness of conventional freeze stabilizing agents when addedthereto.

These objects have been met in a particularly surprising and effectivemanner. In accordance with this invention, it has now been found thatthe freeze resistance or freeze stability of paint latexes produced byemulsion polymerization may be enhanced by the practice of anincremental addition to the emulsion polymerization of one of themonomers of the system. Thus, it has been found that if an aqueousemulsion of a conjugated diolefin and a part of the total to be usedquantity of a monoethylenic monomer polymerizable therewith is subjectedto polymerization to effect a partial conversion of the two monomersprior to the addition of the remainder of the monoethylenic monomer, asubstantially improved freeze stable latex is obtained.

The method of this invention, as indicated, may be effectively employedin the emulsion polymerization of a conjugated diolefin with amonoethylenic compound polymerizable therewith. By conjugated diolefinis meant monomers such as butadiene-1,3, methyl-2-butadiene-L3,chloro-2-butadiene-l,3, piperylene, 2,3-dimethyl butadiene-l,3 and thelike. By monoethylenic compound, it is intended to include thosemonomers having a single CH =C group polymerizable with a diolefin, forexample, aryl olefins such as styrene, vinyl naphthlene, methylstyrene,pchloro-styrene, vinyl toluene, divinyl benzene and the like; methylenecarboxylic acids, their esters, nitriles and amides such as acrylicacid, methyl acrylate, methylmethacrylate, acrylonitrile,methacrylonitrile, acrylamide, methacrylamide and the like; vinylaliphatic compounds such as the vinyl halides, vinyl acetate, methylvinyl ether, methyl vinyl ketone and the like; and vinylidene compoundssuch as the vinylidene halides.

According to the invention, a total of about 58-75% by weight ofmonoethylenic monomer is polymerized with about 4225% of conjugateddiolefin in an aqueous medium. Except for the amounts of monomersinitially introduced into said medium, its contents and method ofpreparation are conventional and well known to those skilled in the artof preparing paint latexes. The emulsion system may be prepared in aconventional manner using any of the well known and commerciallyavailable anionic and nonionic emulsifiers or various combinationsthereof in amounts such as are generally known and practiced. Inaccordance with this invention, however, the emulsifier may be added tothe polymerization system in toto, initially, or it may be incrementallyadded as will be more fully described below with respect to a preferredembodiment of this invention. Representative of emulsifiers which may beemployed in the method of this invention are the water soluble salts ofmonocarboxylic acids, the water soluble salts of hydrogenated,dehydrogenated and disproportionated rosin acids, any of variouspolyether alcohols such as alkyl phenoxy polyoxyethylene ethanols, anyof various water soluble salts of aryl sulfonates such as thealkyltoluene and alkylnaphthalene sulfonates, and the like.

As is usual practice in the emulsion polymerization of such monomers,the polymerization system will also comprise an electrolyte which may beany of various water soluble salts such as sodium or potassium sulfate,tripotassium phosphate, sodium pyrophosphate and the like used inconventional quantities. Similarly, the system will include an initiatorwhich may be a water soluble salt of a persulfuric acid such as sodiumor potassium persulfate. In addition, any of the well known alkylmercaptan modifiers may be employed in the system if desired. The pH ofthe aqueous phase of the emulsion system will be alkaline, ranging to ashigh as 11, although it is preferably maintained somewhat lower, whilereaction temperature it generally in the range of about 150-165 F.

In accordance with one aspect of the method of the present invention, anemulsion polymerization system is initially prepared using all of theabove mentioned components excepts a portion of the monoethyleniccompound which is withheld for subsequent addition. Polymerization isinitiated and conducted to a preselected degree of conversion ofmonomers to polymer, after which the remaining portion of themonoethylenic compound is added and polymerization continued tosubstantially 100% conversion, in accordance with this invention, it hasbeen found that the extent of monoethylenic monomer initially withheldhas a direct bearing on the freeze resistance properties of theresultant latex. It has been observed, for instance, that improvedfieeze resistance properties are obtained when as little as about byWeight of the monoethylenic monomer is withheld for subsequent addition.Below this limit, however, the improved freeze resistance properties ofthe resultant latex obtained according to this invention rapidlydecline. This amount of withheld monoethylenic monomer may be increasedconsiderably, with ever increasing freeze resistance properties beingnoted, to as high as 50%. Beyond about 50%, various properties of thefilms produced from the resultant latex appear to be adversely affected.The amount of monomer Withheld, therefore, will generally not exceedabout 50% and will usually be in the range of about -50%.

The extent to which the initial charge of monomers is converted also hasa bearing on the freeze resistance properties of the resultant latex. Tothis end, it has been found that the conversion of an initial charge ofmonomers may be carried out to a minimum of about although conversionwill usually be to about -90% After initial conversion has beencompleted to the preselected degree, the remaining withheld monomer isadded to the system. This addition may be carried out in the form of asingle batch addition or as periodic incremental additions. Preferably,however, it is conducted as a substantially continuous addition at asubstantially fixed rate. This leads not only to a latex of inherentlyimproved chemical and mechanical stability in addition to improvedfreeze stability, but also to an enhanced effectiveness of any ofvarious post stabilizers usually employed to obtain maximum stability.While the rate of addition of withheld monomer may be quite widelyvaried, it has been found that excellent results are obtained using anaverage addition rate of about 10-30% of the total weight of withheldmonomer per hour. Smaller percentage-rates may be used, but theyprotract the time required to complete the reaction. Larger percentagerates may also be used, but the improvement in freeze resistance may beless pronouncd in many cases.

As indicated previously, the entire emulsifier system may bernade partof the initial charge, the description heretofore of the method of thisinvention being based on such practice. It has been additionallydiscovered, however, that the freeze stability of latexes preparedaccording to the instant method is also influenced by an initial 4withholding of a portion of the emulsifier. The total amount ofemulsifier employed in any polymerization will depend, of course, uponthe particular emulsifiers involved as well as other variables wellknown to those skilled in the art. For the purpose of this invention,the total amount of emulsifier will be that generally employed in knownemulsion systems. The amount withheld from the initial charge inaccordance herewith, however, will vary as the withheld quantity ofmonoethylenic monomer, the percentage of withheld emulsifier generallybeing somewhat greater than the percentage of withheld monomer. Thus,the amount of withheldemulsifier may be as little as about 20%increasing to as high as the usual practice, however, being to withholdabout 20-40%. The subsequent addition of withheld emulsifier, likewithheld monomer, is preferably made in a substantially continuousmanner at an average rate of about 0.05-0.20 parts/hour/ parts totalmonomers, preferably about 0.10-0.15 parts/hour, although the advantagesof this invention may be also realized to varying degrees using otherrates. The preferred degree of conversion to be attained prior to addingthe withheld emulsifier is about 25-60% by weight of the monomers.

A particular feature of this invention associated with the withholdingof part of the emulsifier is that much improved freeze resistance isobtained at lower monomer withholding percentages than when all theemulsifier is initially added. For instance, Whereas the improvement infreeze resistance rapidly declines if less than about 30% of themonoethylenic monomer content is withheld and the entire emulsifiercontent is in the initial charge, for instance, excellent improvement isrecognized when as little as about 10% is withheld if there is also awithholding of emulsifier. When withholding emulsifier, therefore, therange of withheld monomer will usually be less than when no emulsifieris withheld varying from about 10-30%, and the preferred degree ofconversion to be attained prior to adding the withheld monoethyleniccompound is about 70-90%.

The following examples further illustrate the invention. All parts areby weight unless otherwise indicated.

EXAMPLE 1 The following ingredients are charged in a manner subsequentlydescribed to a polymerization reactor.

Ingredient: Parts Monomers- Styrene 67 Butadiene 33 Emulsifiers PluronicL-64 (a condensate of ethylenic glycol with a hydrophobic base formed bycondensing propylene oxide with propylene oxide with propylene glycol, a

A plurality of polymerizations are conducted in which all of therequired charge water, activator, emulsifier and butadiene are chargedto the polymerization reactor. Styrene is withheld in varying amounts asindicated in Table I. The temperature is raised to F. and polymerizationis initiated. When conversion reaches 70%, the remaining styrene isintroduced at a rate of 4.7 parts/ hour. When the reaction reaches 100%conversion, it is cooled and the post stabilizers added.

Four slurries of the following composition are then prepared by mixingthe ingredients in a colloid mill.

Ingredient: Parts Rutile TiO (pigment) 100 Lithopone (pigment) 100 Mica(pigment) 25 Clay (pigment) 75 Tetra sodium pyrophosphate (pigmentdispersant) 2 Casein solution (pigment dispersant) 192 Pine oil(anti-foaming agent) 4 Water 112 TABLE I Withheld Styrene Freeze CyclesWithstood (Percent by Weight) Without Coagulation EXAMPLE 2 Theprocedure of Example 1 is repeated except that emulsifier and styreneare withheld in varying amounts as indicated in Table II. Whenconversion reaches 60%, the remaining emulsifier is introduced at a rateof 0.14 part/hour, per hundred parts total monomers. At 70% conversion,the remaining styrene is introduced at a rate of 4.7 parts/hour. Paintcompositions are prepared from the latexes as in Example 1 and tested astherein. Results appear in Table 11.

TABLE II Withheld Withheld Freeze Cycles Emulsifier Styrene withstood(Percent (Percent Without by Wt.) by Wt.) Coagulation It is to beunderstood that the above examples are illustrative only and not by wayof limitation. The method of this invention may be just as readilypracticed realizing similar advantages using other ratios of butadieneand styrene within the range recognized by the art as applicable for theproduction of paint latex, as well as when using other diolefins and/ormonoethylenic monomers copoly-merizable therewith. It should also berecognized that similar results to varying degrees are realized whenoperating at other withheld amounts and ratios of emulsifier andmonoethylenic monomer particularly when within the ranges specifiedherein, as well as when operating at other initial monomer conversionvalues. Other activators, emulsifiers, post stabilizers, and the like aswell as the amounts thereof may be varied as is well known in the artwithout detracting from the advantages hereof.

We claim:

1. A method for producing an aqueous paint product having the requisitefieeze-thaw stability for withstanding without coagulation twofreeze-thaw cycles in which a sample is subjected to 16 hours atsub-freezing temperature and is then allowed to thaw to roomtemperature, said method comprising: forming an initial aqueous emulsionsystem for polymerizing about 42-25% by weight of a butadiene 1,3 andabout 58-75% by weight of at least one aryl olefin having a single CH =Cgroup polymerizable therewith, said initial emulsion system consistingessentially of emulsifier, all of said butadiene 1,3 and part of saidaryl olefin, about 10-50% by weight of the total of said aryl olefin tobe polymerized with said butadiene 1,3 being withheld from said emulsionsystem and the remainder of said aryl olefin being included in saidemulsion system; subjecting said emulsion system to polymerization toeffect an initial conversion of about to about 90% by weight of saidmonomers; thereafter adding said withheld aryl olefin to the resultantemulsion system; further polymerizing until substantially 100% by weightconversion of monomers is obtained; and colloidally dispersing paintpigment, pigment dispersant and anti-foaming agent in the resultantsynthetic polymer latex.

2. A method for producing an aqueous paint product having the requisitefreeze-thaw stability for withstanding without coagulation twofreeze-thaw cycles in which a sample is subjected to 16 hours atsub-freezing temperature and is then allowed to thaw to roomtemperature, said method comprising: forming an initial aqueous emulsionsystem for polymerizing a total quantity of about 42-25% by weight of abutadiene-1,3 and about 58-75% by weight of styrene, said initialemulsion system consisting essentially of emulsifier, all of saidbutadiene and part of said styrene, about 1050% by weight of the totalquantity of said styrene to be polymerized with said butadiene beingwithheld from said emulsion system and the remainder of said styrenebeing included in said emulsion system; subjecting said emulsion systemto polymerization to effect an initial conversion of about 60% to aboutby weight of said monomers; thereafter adding the withheld styrene tothe resultant emulsion system; further polymerizing until substantiallyby weight conversion of monomers is obtained; and colloidally dispersingpaint pigment, pigment dispersant and anti-foaming agent in theresultant synthetic polymer latex.

3. A method according to claim 1 in which the withheld monoethyleniccompound is added in a substantially continuous manner at asubstantially fixed rate.

4. A method according to claim 1 in which the total quantity of emulsionis added to the initial emulsifier system.

5. A method according to claim 1 in which the amount of withheld arylolefin compound is about 30-50% by weight of the total to be employed.

6. A method according to claim 5 in which the withheld aryl olefincompound is added in a substantially continuous manner at asubstantially fixed rate.

7. A method according to claim 6 in which said conjugated diolefin isbutadiene and said aryl olefin compound is styrene.

8. A method according to claim 7 in which said rate is about 10-30% byweight per hour of the total withheld styrene.

9. A method according to claim 7 in which said initial conversion isabout 60%-90% by weight.

10. An aqueous paint product containing the product of claim 2.

References Cited UNITED STATES PATENTS 2,745,818 5/1956 Te Grotenhuis26O-880 2,754,282 7/1956 Stoops et al. 260880 2,767,153 10/1956 Sutton26029.6 2,822,341 2/1958 Miller et al. 260-83.7

(Other references on following page) 7 UNITED STATES PATENTS Childers eta1. 26029.7 Fordham 260880 Kolaczewoski et a1. 260-25 Brock 260-880Zdanowski 260880 Te Grotenhuis 26029.7 Huber 260880 8 3,267,061 8/1966Senior et a] 260-29.7

3,282,867 11/1966 Stahly et a1. 26029.6

MURRAY TILLMAN, Primary Examiner.

5 G. F. LESMES, Examiner.

J. T. GOOLKASIAN, I. ZIEGLER, Assistarzt Examiners.

